(Reuters) - Washington, D.C., ethics expert Mark Foster of Zuckerman Spaeder went to bed Sunday night mulling the question of whether President Donald Trump’s personal lawyer, John Dowd, could be subpoenaed by a grand jury to testify about a tweet Saturday from the president’s Twitter account that said Trump fired his national security adviser “because he lied to the Vice-President and the FBI.”

By Monday morning, Foster told me, the answer seemed clear to him: If special counsel Robert Mueller wants to hear Dowd’s account of the controversial tweet, Dowd won’t be able to claim attorney-client privilege to avoid testifying.

Mueller is investigating Russian attempts to influence the 2016 U.S. election and potential collusion by Trump aides. Russia has denied meddling in the election and Trump has said there was no collusion. On Friday, former Trump national security adviser Michael Flynn pleaded guilty to lying to the FBI in an interview last January.

Dowd and White House officials made a tough issue easy, Foster said, by disclosing over the weekend that Dowd – and not the president – actually wrote the tweet, and then revealing additional details Monday about its drafting and publication. Ordinarily, of course, collaboration between clients and lawyers is privileged, even when lawyers make public statements on behalf of their clients.

So why might Mueller’s team want to know more about the notorious tweet? The tweet created a hullabaloo over the weekend after several legal experts said it suggested that the president knew his national security adviser had lied to the FBI before Trump allegedly asked then FBI director James Comey to go easy on Flynn. The president adamantly denies that he asked Comey to stop investigating Flynn, but his critics seized on Saturday’s tweet as evidence Trump was trying to impede a criminal investigation of his national security adviser.

That narrative was quickly undercut when Dowd said that he, and not President Trump, had drafted the tweet – and that he’d made “a mistake” in his account of the president’s knowledge. Dowd told Reuters he erred in saying in the tweet that the president knew Flynn had lied to the FBI at the time of Flynn’s firing. According to Dowd’s statements on Sunday, Trump first learned for sure that Flynn had committed a crime only when the former national security adviser pleaded guilty on Friday.

“The mistake was I should have put the lying to the FBI in a separate line referencing (Flynn’s) plea,” Dowd told Reuters. “Instead, I put it together and it made all you guys go crazy.”

According to Foster, President Trump effectively waived the privilege by allowing Dowd and other White House officials to disclose how the tweet got out because their comments revealed attorney-client privilege.

Just because Mueller could seek Dowd’s testimony doesn’t mean that he will. In the Whitewater investigation of President Bill Clinton, independent counsel Kenneth Starr went to court to compel testimony from a lawyer for Monica Lewinsky. The lawyer and Lewinsky tried to quash the grand jury subpoena by claiming privilege. The District of Columbia U.S. Court of Appeals ended up siding (162 F.3d 670) with Starr because of evidence Lewinsky was attempting to obstruct justice by submitting a false affidavit in the Paula Jones case. (According to the D.C. Circuit, the lawyer who drafted the affidavit was blameless; Lewinsky allegedly gave him a false account of her relationship with Clinton.)

Mueller’s team, you may recall, has also used the crime-fraud exception to compel testimony from a private lawyer. After former Trump campaign officials Paul Manafort and Richard Gates were indicted in October, Politico reported on a newly unsealed court decision that indicated prosecutors cited the exception to enforce a subpoena for testimony from a lawyer who advised Manafort and Gates on responding to inquiries about their lobbying registration.

There is precedent, in other words, for special counsel to pierce privilege – but prosecutors don’t do it lightly. Think of all of the times lawyers issue statements defending their clients. That’s a huge universe. Now think of all the times prosecutors have demanded testimony about the privileged communications underlying lawyers’ statements. I bet you’re struggling to think of any.

Still, after Dowd claimed responsibility for drafting the tweet, Theodore Boutrous of Gibson Dunn & Crutcher suggested (on Twitter, of course) that Dowd’s account of the tweet’s history “seems like a privilege waiver and an invitation to the Special Counsel to interview or subpoena the lawyer.”

There’s no precedent for these precise circumstances, Boutrous said when I called him to follow up on Sunday. But he drew an analogy between President Trump and clients asserting an advice-of-counsel defense. To blame their lawyers, defendants typically have to waive privilege. If the president is contesting the accuracy of Saturday’s tweet by laying responsibility on his lawyer, Boutrous said, Mueller’s prosecutors could argue they have a right to test the assertion.

Lawyers on both sides tend to regard attorney-client privilege as a fundamental tenet of the criminal justice system. If Mueller’s team tries to compel the disclosure of communications between the president and his private lawyer, it will be because these longtime public servants believe there’s a really good reason to do so.